Problem: My fish doesn't seem well after I moved it to a new tank. I'm afraid it's because of the rocks(it's bright yellow and I didn't buy it from a pet store)or the water quality. What it does differently is that it bangs around the tank every now and then.. and I gave him couple of dry worms (Which I've been feeding ever since November) and it would only eat half of it.. really slowly too. It usually eats everything in a minute but this time it took almost 15 minutes

What I've done so far...
So my friends gave me a betta fish on my 19th birthday back in November. I Kept it in a small plastic container (the ones you get from the pet store) and then that broke around March so then I changed it to a 3L water bottle. Back in December I got the fish some neon colored ( a mixture of bright yellow, pink, green, orange and blue) gravel and a plastic plant from a pet store near my dorm. And then yesterday I went to a furniture/interior store and found this bowl(it's supposed to be used for candles) and some yellow marbles or something. Usually I use tap water and mix that with some neutral regulator. However I ran out of the powder so I used fiji water instead. I've used fiji water before and it didn't affect my fish so I figured it wont be bad. I set up the tank last night and let it sit overnight so that the temperature can goto room temperature. I then placed the fish in the bowl but initially it hit itself against the bowl and then just laid sideways on the rocks. Now it just swims around with it's head almost touching the surface.

I never had a betta fish before and so I don't know what to do. Should I put it back in the bottle? Is it the bright yellow rocks that's disturbing the fish. Please help!

IMO Please get something bigger, at least 1 gallon or so. However I prefer at minimum, 2.5. But above that, I really prefer and would recommend something around 5 gallons, give or take a gallon.

For water:1. Should be heated to 77-80F. 75 is already pushing it. Bettas are tropical, so they need warm waters. I have no idea how to safely heat something as small as that, though, which is why larger tanks are much more easier to manage in terms of that. By some water conditioner, like Seachem Prime, and use this with your regular tap water. (Instructions on Prime are straightforward). It works immediately, too. Whenever you change water, also try to match up temperature from old tank water and new water to prevent shock.

2. The trashing... could be an external parasite, and he's trying to shake it/ hit it off. Or...he's uncomfortable, but I can't really prove the latter. His clamped fins are definitely a sign of something. Could be everything ,stress/boredom, illness, water temperature, etc. He could have damaged his swim bladder, causing swim bladder disorder, making him float. Usually this goes away in time.

How often are you doing water changes? IMO in something like that, it should be daily.

Also, the dry worms...they must be freeze-dried, right? Maybe freezedried bloodworms? I've heard these are high un-nutritional and is more like candy. Pellets make a much better staple as they're a lot more nutritional for him, and will help him with his immune system. I use Hikari Bio Gold and it's doing well for me.

Ok thanks! About the size, I live in a dorm.. and I'm not allowed to have a fish in the first place (don't ask me why my friends decided to buy me a fish for my birthday).. I'll keep that in mind when I move off campus next year though.
I clean the tank at least once a week.. if not twice. I need to keep it low key cause my RA can take the fish away. Hopefully my fish will pull through for another month before I move out of this place :(

Ahh I see. I can definitely imagine my friends buying me a dog if I lived in a dorm, haha.

I would suggest you do water changes much more often, and definitely keep him somewhere warm. If you're not money tight, you can get a Hydor Mini Heater, but I don't even know how big that is. Are you absolutely sure you cannot fit him into anything bigger? Also I'll just say again, get some pellets for him as freezedried anything doesn't do much on a daily basis.